1. Field of the Invention
The present invention relates to mobile telecommunication devices and, more particularly, to raster skipping in co-banded mobile communication devices based on previous scans for any band.
2. Description of the Related Art
Historically, mobile phones have been designed to operate using one access technology, such as Global System for Mobile communication (GSM), Code Division Multiple Access (CDMA), or Time Division Multiple Access (TDMA). Each of the different access technologies utilize a defined set of protocols and techniques to communicate wirelessly over a characteristic set of frequencies of the electromagnetic (EM) spectrum. These frequencies are a valued and finite resource. To maximize usage, reusing spectrum frequencies is common, which is true even among different access technologies. For example, different access technologies can share a portion of the EM spectrum. The wideband version of CDMA (WCDMA), for example, overlaps significantly with GSM frequency ranges. All of the actively used GSM bands have a WCDMA equivalent defined in the latest version of the 3GPP specifications. Co-banded mobile phones currently exist that operate seamlessly across frequency ranges of more than one access technology using suitable protocols for communicating via each supported access technology. For instance, a co-banded mobile phone can support both GSM and WCDMA based communications. Appreciably, co-banded mobile phones are not limited to GSM and WCDMA technologies. Co-banded mobile phones and other mobile communication devices exist currently and more will exist in the future that support two or more access technologies, each of which requires periodic raster scanning.
It should be appreciated that mobile phones scan a set of channel segments to find occupied bands associated with a particular access technology and mark those bands that are discovered. A smallest scan-able channel segment that is able to be used for a communication can be referred to as a communication raster. A communication raster composition and specifics can vary based upon an access technology. For example, a Frequency Division Multiple Access (FDMA) access technology (e.g., CDMA) shares the radio spectrum by allocating users different carrier frequencies of a radio spectrum. TDMA access technologies (e.g., GSM, TDMA) allow several users to share the same frequency channel by dividing the signal into different timeslots, each user using their own timeslot. A Space Division Multiple Access (SDMA) takes advantage of spatial separation between users by subdividing a base station's coverage area into sub-cells and by using directional transmissions to and from a mobile phone so that different spatially located mobile phones can share a frequency channel. Shifting phases is still another technique for dividing a single frequency channel into multiple segments, each of which can be used by a different user to wirelessly communicate.
Regardless of which access technology or technologies are being used, scanning for an available communication raster occurs in approximately the same manner. Conventional scanning occurs by ordering the rasters by power level in descending order and checking each one. Checking a raster can require decoding, which determines whether communications are able to be conducted using that raster or not. The ordered rasters are sequentially checked and decoded. If no occupied raster is detected for a given access technology during scanning, the scanning process can be reattempted after a delay period.
The large number of rasters resulting from a generous frequency ranges being allocated to different access technologies presents a problem for co-banded mobile phones. Scanning each raster in all frequency ranges for each access technology can result in excessive power usage, which can drain the batteries of handsets. Additionally, the time required to scan through multiple frequency bands increases dramatically from phones that operate in a smaller frequency band, which have to search fewer rasters. This increased scanning time can result in dialing delays, such as a scanning delay that occurs on device power-up, that frustrate users. In areas of dense usage, such as cities, scanning for all communication rasters can be extremely resource intensive. It would be advantageous if scanning times and resource use could be reduced through intelligent raster skipping in co-banded mobile phones, which is not presently being done by any known mobile device.